Heart attacks constitute one of the major sources of incapacitation or death to human beings. Such failures often result from blockages in coronary arteries that are due to the accumulation of plaque on the arterial walls. Such accumulations of plaque gradually block the flow of blood through the arteries to the heart until there is a complete stoppage or almost a complete stoppage in the flow.
In addition to the problems incurred by blockages in coronary arteries, blockages of other arteries can also cause incapacitation or death to human beings. Plaque buildup in the arteries of the arms or legs can result in limb amputations. Plaque buildup in the arteries of the head and neck can result in strokes. Plaque buildup in the arteries of the kidneys can result in hypertension (high blood pressure). Additionally, plaque buildup in other peripheral (non-coronary) arteries can result in degradation of the organs which they supply.
Until relatively recently, it has been difficult to diagnose and detect the accumulation of plaque in the arteries of living beings. In recent years, techniques have been devised for detecting and locating accumulations of plaque on the arterial walls of living beings. Indeed, these techniques have become so advanced that it is now not uncommon to advance probes completely through the arteries to locate and estimate the relative amount of arterial blockage at such progressive positions along the artery.
Several techniques have also been developed to correct for blockages in the arteries of living beings. One well known technique which is often used is the so-called bypass surgery. In bypass surgery, the blocked portion of an artery is shunted using a segment of a vessel from another part of the body of the afflicted human being.
Bypass operations, however, can be of considerable danger to the living being undergoing the operation. One reason for this concern is that the living being has to be cut open to expose and treat the diseased site. The patient also has to undergo anesthesia, the effects of which are often unpredictable. Together, the trauma resulting from the anesthesia and the opening of the body of the living being presents a grave danger to the patient.
Angioplasty techniques have also been developed in recent years as a means to alleviate blockages in the arteries in living beings. As is well known, angioplasty procedures involve the insertion of a deflated balloon into the artery of the living being. The balloon is then moved, as by a conduit, to the blocked position. Thereafter, the balloon is inflated to expand the diameter of the artery and enlarge the passageway through the artery. In this manner, the plaque is at least partially broken up to thereby alleviate the blockage.
Angioplasty procedures, however, have certain inherent disadvantages. First, expansion of the arterial wall at the blocked position stretches, and thereby weakens, the arterial wall. This alone may cause adverse consequences. Further, since plaque blocking the artery is often calcified and quite hard, it can be difficult, and sometimes impossible, for the balloon to overcome the counterforce exerted by the plaque against the balloon. Still further, and very importantly, angioplasty procedures do not remove plaque from the artery. This is particularly troublesome since the obstructive tissue which remains in the artery creates a condition conducive to the creation of another blockage. Thus, it can be a recurring problem. Importantly, unlike angioplasty, atherectomy procedures cut the plaque, or other obstructive tissue, from the inside of the artery to create a passageway through the plaque. No expansion of the arterial wall is required.
As can be easily appreciated, not only must the atherectomy system employed be effective in cutting and removing plaque, it is essential during such a procedure that the cutting device be carefully controlled and not be allowed to cut through the arterial wall. For the present invention, the necessary control is provided by the concerted effort of a control unit which operatively positions the cutting device within a support sheath and a guide wire which establishes the path of the cutting device.
Several examples of guide wires have been previously disclosed. Typical of these examples are U.S. Pat. No. 3,731,671 which issued to Mageoh for an invention entitled "Low-Friction Catheter Guide" and U.S. Pat. No. 3,789,841 which issued to Antoshkiw for an invention entitled "Disposable Guide Wire." Further, the use of a guide wire for a rotary catheter system has been disclosed in U.S. Pat. No. 4,732,154 which issued to Shiber. All of these guide wires, however, are intended to do no more than provide a means to position the operative medical device over the positioned guide wire.